Development in the semiconductor industry has resulted in increasingly compact and complex system circuitry. There is an ever-increasing challenge to prevent thermal breakdown in components that is due to inadequate power management. Thermal stress puts a lid on processor clock rates, reduces component life, and results in costly maintenance requirements and cooling applications. Several attempts have been made to address thermal power management requirements.
Generally, a thermal management system may have zero or more sensors. The sensor for a given component or components either measures power dissipation or consumption or derives it from other measurable quantities such as temperature, current, voltage, or pressure. In addition, a system must know the desired amount of average power dissipation so that it can compare this amount against the measured power dissipation to exert some form of thermal control. This invention provides several methods of controlling the average power dissipation of an electronic component.
The period of time over which the power is averaged is a critical factor in determining the most appropriate method to use. For example, if the primary concern is heat dissipation, then it may be reasonable to average the power for many milliseconds or even full seconds. However, if the primary concern is current spikes, then the power may be averaged over only 100 nanoseconds or less. While many methods discussed here are applicable to the former situation, the latter is much more difficult.
U.S. Pat. No. 5,477,076 issued Dec. 19, 1995, and U.S. Pat. No. 5,376,819 issued Dec. 27, 1994, both to Gay et al., disclose an integrated circuit that implements a thermal circuit on a chip for measuring temperature of an operating integrated circuit die with only one dedicated integrated circuit pin. A second integrated circuit pin is connected directly to other circuitry on the integrated circuit and is used by the other circuitry at the same time that the integrated circuit die temperature is measured. In one form, the second integrated circuit pin is a ground terminal. Error voltages coupled to the ground terminal may be removed from the temperature calculation by an external differential amplifier.
U.S. Pat. No. 5,230,564 issued Jul. 27, 1993 and U.S. Pat. No. 5,281,026 issued Jan. 25, 1994, both to Bartilson et al., disclose a monitoring system for air-cooled printed circuit boards that utilizes temperature sensors having thermal diodes embedded directly into the integrated circuits. The thermal diodes are part of the fully-functioning integrated circuit. As they are driven by voltages on the board, they require no added power sources. The thermal diode has a voltage inversely proportional to the temperature. It can be calibrated to convert a given voltage into a given temperature. This conversion can be utilized by a logic controller to monitor and control cooling. Pressure sensors are also used with the temperature sensors to monitor air pressure along the ducts leading to the printed circuit boards. Pressure sensors are also driven by voltages from the board. They have an amplification circuit to increase the signal. The pressure reading can also be utilized by a logic controller for controlling and monitoring the cooling of the boards.
U.S. Pat. No. 5,213,416 issued May 25, 1993, to Neely et al. discloses a novel on-chip temperature sensing circuit that includes a differential voltage source that comprises a plurality of branches, each of which has a temperature-sensitive transistor. The output from the differential voltage source is coupled to the high-gain differential amplifier whose outputs are connected to a second-stage differential amplifier. One of the branches of the second-stage differential amplifier is coupled to a high-gain transistor amplifier that is in turn connected to an output pin on the semiconductor chip, so that the signal at the output pin is a noise-tolerant voltage indication of the temperature of the semiconductor chip, which may be monitored during actual on-line operations. The two differential amplifiers may be coupled to provide a hysteresis feedback loop and rapid switching of the second differential amplifier.
U.S. Pat. No. 5,639,163 issued on Jun. 17, 1997, to Davidson et al. discloses a pair of on-chip thermal sensing diodes formed together and interconnected with a common cathode to form a differential sensing pair. A pair of precision resistors external to the chip generates two constant currents, one for each diode, with a ratio on the order of 100 to 1. The precision resistor values are selected so that variations about the nominal values of metal and via resistances between the diode contacts and the chip contact pads are negligible compared to the precision resistor values. Leads, connected respectively to two pads on the chip, couple a differential output of the anode voltages of the diode pair to the input of a high-impedance amplifier.
U.S. Pat. No. 5,660,474 issued Aug. 26, 1997, to Kurihara discloses a temperature detecting circuit that generates an output signal that depends on temperature and is unaffected by variations in power supply voltage. The temperature-detecting circuit provides a diode that generates across two terminals a voltage that depends on the temperature, a first resistor connected to the anode of this diode, a second resistor with one end grounded, first and second transistors for applying a fixed voltage to the first and second resistors, third and fourth transistors supplied by the current flowing through the first and second resistors, fifth and sixth transistors to the bases of which the emitter currents of the third and fourth transistors are applied, and seventh and eighth transistors to the bases of which the emitter currents of the fifth and sixth transistors are applied. The output current varies with the temperature but not with the power supply voltage.
More recently, another hardware thermal sensing/monitoring system was introduced by Maxim Integrated Products of Sunnyvale California ("IC keeps tabs on hotter CPUs," Electronic Engineering Times Feb. 2, 1998,). The Maxim component reads temperatures at the surface of the die by measuring temperature-induced changes in the forward voltage across a diode or transistor junction, then it linearizes and converts the voltage changes to a serial digital signal. The Maxim component does not require special temperature sensors or physical attachment to heat sinks. A reading through a pn diode or transistor is taken from the chip itself through voltage measurements across two chip pins. Base-emitter voltage is measured across a diode or transmitter on the CPU die. Two controlled-current sources force current into pinouts provided at the CPU, then read the voltage difference across them. An on-chip AID converter makes this a digital reading, which is fed concurrently to an SMBus transceiver and a bank of internal registers. These registers can also store reference values and can trigger external shutdown or pulse-skipping mechanisms for the processor.
In addition to the previous hardware implementations there are numerous methods of reducing power dissipation of a processor. One means used in the art is a "sleep mode" whereby the processor is suspended in a low power mode awaiting a "time ouf" or "interrupt" to "wake up." Another means is "pulse skipping" whereby a processors clock that is typically a uniform, periodic train of pulses is modified to occasionally omit a pulse.
None of the prior-art solutions provide for a coordinated power management system for multiple components. What is needed is a system or method of providing thermal control to a plurality of processors or components intelligently based on overall system processing needs. Such a system is also desirable when thermal control can be achieved without a major modification of existing circuitry or a large departure from system design. Furthermore, a system or method of monitoring thermal behaviors of plural processors or components would be a desirable enhancement in such a control system. Features of the present invention are presented that achieve thermal management, monitoring, and control in a manner that addresses the needs of complex systems. With the present invention, a flexible control system for intelligent power management of numerous processors is provided.